Does anyone know of a chemical that will kill pond weed moss and cat tails?
The weeds and grass are so thick in my pond that is impossible to fish it from the bank. I would appreciate any advice and comments

Aquathol K is effective for treating American Pondweed - the weed with the narrow pointed leaves that float on the surface in shallow areas. However, the product is too expensive to treat ponds larger than 1/2 acre. As for weed moss - Cutrine Plus works pretty well on Filamentous Algae, but not sure about Chara (Muskgrass). I've had cattails in profusion in a couple of ponds, but have never attempted to treat it. The cattails slowly disappeared after a few years. Maybe the Aquathol K that was used to treat the pondweed also had an effect on the cattails.

Cattail question posed here just a couple weeks ago.

How to get rid of Cattails.

Not exactly sure what you are calling Pond Moss, but likely filamentous Algea. Cutrine is your best chemical option. Tilapia can control it if you stock in high enough qty's. You can always visit this site to determine what you have and then methods to treat it.

https://aquaplant.tamu.edu/

+1
Identify what kind of pondweeds you have then find out what works on those weeds.
If you kill too much at once in this summer heat, it can use up the dissolved oxygen in the water and cause a fishkill

I wish would have see this earlier I have used a Glyphosate based chemical, rodeo not bad. I would avoid a Diquat based in that it is contact kill, it may be hard to reach the plant. Imazapyr can be used and does a good job, it bonds to water rapidly and stock can drink from it with out a waiting period. all chemicals will cause decay and if there is large amounts of decay could effect o2 levels. low o2 can produce a fish kill. I have burned cattails at low water levels and then treat them, to reduce biomass and limit decay, after chemical treatment. good luck

Glyphosate or Imazapyr plus microbial will control and reduce your biomass of cattails. Works effeciantly on cattails and lotus. Diquat is a contact herbicide but you msut use a good surfactant to make it stick to target species-contact herbicide.